You can find video tutorials for your iPod here: http://ipodhowtovideo.com/
As burf says, searching youtube or other video sites will have tonnes of information. There are lots of models that come in 30g, but if its 4th or 5th gen 'video' ipod, its easy. you just need a razor blade, or sharp plastic ipod opening tools to gently pry the metal sides away from the plastic face of the ipod. Once open, the battery should unplug/replace or might need desoldering a few wires.